[Bug tree-optimization/84515] missed optimization: expected loop merging

[law at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84515

Jeffrey A. Law <law at redhat dot com> changed:

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                 CC|                            |law at redhat dot com

--- Comment #4 from Jeffrey A. Law <law at redhat dot com> ---
The degenerate PHI is a bit of a red-herring.  It's turned into a degenerate
via uncprop to discourage the unnecessary constant initialization.

Really the key here is we need to know the relationship between _20 and
count_11.  

That relationship is that count_11 >= _20

But EVRP never gives us that symbolic relationship so threading really never
gets a chance.